Pendulous assembly for use in an accelerometer

ABSTRACT

A pendulous assembly for use in an accelerometer or other such devices which senses forces acting on the device in a particular direction is disclosed herein. This assembly includes a proofmass and an arrangement supporting one end of the proofmass for pivotal movement back and forth about a given axis through a resting plane which entirely contains the proofmass when the latter is at rest. The support arrangement itself includes a frame, an isolation bridge or bridges and an arrangement of isolation bridge and proofmass flexures for supporting the isolation bridges between the proofmass and frame.

This is a division of Ser. No. 07/221,116, filed July 19, 1988, now U.S.Pat. No. 4,955,233, which is a continuation-in-part of Ser. No.06/899,975, filed Aug. 25, 1986, now abandoned.

This invention relates generally to a device such as an accelerometerfor sensing forces acting on the device in a particular direction, andmore particularly to the pendulous assembly for use in such a device.

In the above-recited co-pending application (hereinafter referred to as"Applicant's Parent Application"), there is disclosed (in FIG. 1) atypical prior art accelerometer which uses a pendulous assembly of thegeneral type to which the present invention pertains. That accelerometerincludes upper and lower magnetic structures having pickoff plates and apendulous type of proofmass assembly therebetween. The proofmassassembly is comprised of a support frame including mounting pads, a reedor pendulum connected to the frame by means of a pair of flexure hinges,and a pickoff plate and torque coil mounted on both the top and bottomsurfaces of the proofmass. The overall device senses acceleration alongan axis normal to the proofmass.

As described in Applicant's Parent Application, any acceleration havinga component along the accelerometer's sensitive axis (which is normal tothe plane of the frame and its proofmass) will cause the proofmass totend to angularly deflect on its flexures, either up or down withrespect to the frame depending on the direction of acceleration.Deflection of the proofmass causes cooperating pickoff plates on theproofmass and on the magnetic structures to apply a signal to sensingelectronics which, in turn, apply restoring current to the torque coilsto return the proofmass to its undeflected (resting) position. Theamount of such restoring current provides a measure of the sensedacceleration, after calibration of the accelerometer and its associatedsensing electronics.

It should be appreciated that the device just described is extremelysensitive to any type of movement of its proofmass. Even randommicromovement that cannot be compensated for may adversely affect theaccuracy of the device. Such movement typically results from internalstresses within the proofmass assembly and stresses imparted to theassembly from the outside world through mounting pads which form part ofthe assembly frame. A source of internal stress may be metallizedelectrically conductive leads between the pickoff plates or torque coilson the proofmass or static electricity dissipation element plates on theproofmass and the outside world. Typically, these electricallyconductive leads are made of different material than the proofmass,frame and flexures and display a different thermal coefficient ofexpansion. This results in what may be referred to as localized bimetalstresses.

It is virtually impossible to eliminate all of the different types ofunwanted stresses from the frame forming part of the proofmass assembly.However, at the same time, such stresses will not adversely affect theoperation of the overall device so long as those stresses do not reachthe proofmass itself. Applicant's Parent Application, recited above,discloses different proofmass assemblies which deal with those unwantedstresses and strains. In particular embodiments (FIGS. 8 and 10) in thatapplication, an isolation bridge is supported by an arrangement offlexures between the assembly frame and the proofmass in order toisolate the proofmass from the frame. As will be seen hereinafter, thepresent application contemplates three additional embodiments.

In view of the foregoing, it is a general object of this invention toprovide a pendulous type of proofmass assembly for use in anaccelerometer or other such device which senses forces in a particulardirection, and specifically a proofmass assembly which isolates itsproofmass from stresses occurring in its frame.

Another general object of this invention is to provide a pendulous typeof proofmass assembly which includes an arrangement of flexuresconnected to and supporting its proofmass for pivotal or deflectingmovement and which also isolates the proofmass supporting flexures fromstresses in its frame.

A more particular object herein is to provide a pendulous type ofproofmass assembly of the last-mentioned type, and specifically anassembly which is designed to cancel out bimetal stresses occurring atthe flexures.

Another object herein is to provide a proofmass assembly which isdesigned to display a high resonant frequency, the low angular springrate, and low loading stresses along the pivot axis of its proofmass.

Still another particular object of this invention is to provide apendulous type of proofmass assembly that supports its proofmass bymeans of a frame and an arrangement of flexures including flexuresconnected directly to the frame which is specifically configured toreduce the amount of stress that reaches any of the flexures from theframe.

As will be described in more detail hereinafter, the pendulous type ofproofmass assembly disclosed herein comprises a proofmass and meanssupporting one end of the proofmass for pivotal movement back and forthabout a deflecting axis through a resting place which entirely containsthe proofmass when the latter is at rest. The supporting means includes(1) a frame and means for mounting the frame to a main support formingpart of a force sensing device containing the assembly, (2) isolationbridge means, (3) isolation bridge flexure means connecting theisolation bridge means with a section of the frame for pivotal movementof the isolation bridge means back and forth about the deflecting axis,and (4) proofmass flexure means separate from and substantiallyunconnected, preferably entirely so, with the isolation bridge flexuremeans. The proofmass flexure means connects the proofmass with theisolation bridge means for pivotal movement of the proofmass back andforth about the deflecting axis.

As will be seen, the isolation bridge means serves to isolate theproofmass and proofmass flexure means from stresses and strains in theframe and isolation bridge flexure means. In two particular embodiments,all of the flexure means and the isolation bridge means are configuredsuch that one entire side of the isolation bridge means isfree-floating. At the same time, electrically conductive leads arearranged on the isolation bridge flexure means and the proofmass flexuremeans supporting the free-floating isolation bridge means to achievebimetal stress cancellation. As will also be seen, in one of these twolatter embodiments, the proofmass and proofmass supporting means arespecifically configured so that the free-floating isolation bridge meansis located between all of the flexure means and a main part of theproofmass such that the overall assembly can operate at a very highresonant frequency and a low angular spring rate and with low loadingstress along its pivot axis.

The various embodiments of this invention, including other features,will be described in more detail hereinafter in conjunction with thedrawings, wherein:

FIG. 1 diagrammatically illustrates, in plan view, a pendulous type ofproofmass assembly designed in accordance with one embodiment of thisinvention;

FIG. 2 diagrammatically shows a section of the assembly of FIG. 1,specifically illustrating a particular operating feature of theassembly;

FIG. 3 diagrammatically illustrates, in plan view, a pendulous type ofproofmass assembly designed in accordance with the second embodiment ofthis invention;

FIG. 4 diagrammatically shows a section of the assembly of FIG. 3,specifically illustrating the particular operating feature of theassembly; and

FIG. 5 diagrammatically illustrates, in plan view, a pendulous type ofproofmass assembly designed in accordance with a third embodiment ofthis invention.

Turning to the drawings, attention is first directed to FIG. 1 which, asstated above, diagrammatically illustrates a pendulous type of proofmassassembly designed in accordance with one embodiment of this invention.This assembly is generally indicated by the reference number 10 and,while not shown, forms part of an overall accelerometer or other suchdevice which senses forces acting on the device in a particulardirection. For a more detailed discussion of the other components makingup such a device, references is made to applicant's Parent Applicationrecited above.

Proofmass assembly 10 is shown including a proofmass 12 and an overallarrangement 14 supporting the proofmass for pivotal movement back andforth about a given deflecting axis 16 through a resting plane in theplane of the paper which contains the proofmass when the latter is atrest, that is, in the absence of any sensing forces. Proof mass 12 isshown supporting a torque coil and pickoff plate, as indicated by thedotted lines at 18 and 20, respectively. These components and similarones on the opposite side of the proofmass are connected to the outsideworld by means of electrically conductive leads generally indicated bydotted lines at 22. These leads are typically made of chrome/gold havinga coefficient of thermal expansion not matching the coefficient ofthermal expanion of the flexure material.

It is to be understood that torque coils 18 and pickoff plates 20 arenot pertinent to this invention other than as a part of the overallaccelerometer or like device and hence, will not be described furtherherein. This is also true for any and all of the other components notshown, but which form part of the overall device. For example analternative to the torque coils, pick off plates and associatescomponents could be a force sensitive vibrating crystal. This inventionis directed to the specific way in which proofmass 12 is supported byarrangement 14 and, in particular, the way in which it is isolated fromstresses in the support arrangement and the outside world generally.

Still referring to FIG. 1, proofmass 12 is shown including a flat,generally rectangular main body 24 having a front elongated edge 26 anda generally parallel back edge 28. Proof mass 12 also includes a pair ofgenerally L-shaped legs 30 and 32 integrally formed with and extendingrearwardly from opposite ends of back edge 28. These legs includecorresponding sections 30A-30B and 32A-32B, respectively. Note thatsections 30A and 32A are normal to edge 28 of main body 24 and sections30B and 32B are parallel with edge 28 and extend toward one another.

Support arrangement 14 includes an overall flat support frame 34 whichcircumscribes proofmass 12. The support frame includes opposing sections36 and 38, connected together by mounting pads 40 which serve to mountthe frame to a main support (not shown) forming part of the overallaccelerometer or other such device. Support arrangement 14 also includesa flat, elongated isolation bridge 42, an isolation bridge flexure 44connecting the isolation bridge with a segment of frame 34 for pivotalmovement of the isolation bridge back and forth about axis 16, and apair of proofmass flexures 46 and 48 connecting proofmass 12 withisolation bridge 42 for pivotal movement of the proofmass back and forthabout axis 16. In a preferred embodiment of this invention, the entireproofmass 12 and the entire support arrangement 14 including frame 34,all the flexures and the isolation bridge are constructed as anintegrally formed sheet or wafer of material, specifically from a singlefused quartz wafer having a thermal coefficient of expansion of nearzero. As in the embodiments described in applicant's Parent Application,portions of this integral wafer corresponding to the flexures are etchedso as to be thinner and therefore more flexible than the proof-mass,frame and isolation bridge. At the same time, the mounting pads 40 maybe designed so that they are thicker than the rest of the frame. Whilethis is a preferred embodiment, it is to be understood that thisinvention is not limited to this integral approach or to the use ofquartz material.

As can be seen in FIG. 1, flexures 44, 46 and 48 are lined up adjacentto one another along axis 16. Flexure 44 supports isolation bridge 42 toframe 34 for pivotal movement about axis 16 while flexures 46 and 48support proofmass 12 to the isolation bridge for pivotal movement aboutthe same axis. In the absence of any forces, for example, accelerationforces, normal to main body 24 of proofmass 12, the proofmass remains atrest in the same plane as frame 34, isolation bridge 42, and flexures44, 46 and 48, all within the plane of the paper.

On the other hand, in the presence of forces normal to the resting planecontaining these components, main body 24 of proofmass 12 deflects aboutaxis 16, either upward or downward depending upon the direction of theforce. It is this movement that is restrained by the torque coils 18,pickoff plates 20 and the associated electronics for measuring theforces that are present at any given moment.

As discussed in applicant's Parent Application, a proofmass assemblythat supports a proofmass to a frame for pivotal movement about a givenaxis by means of flexures is not new. Such an arrangement is generallyillustrated in FIG. 1 in the parent application. However, the particularsupport arrangement 14 forming part of overall proofmass assembly 10shown here includes a number of features which have been designed inaccordance with the present invention to improve the typical arrangementin the prior art. These various features will be discussed below, one ata time. For the moment, it suffices to say that all of the features ofsupport arrangement 14 rely on the use of isolation bridge 42 and itsassociated isolation bridge flexure 44 which do not form part of thetypical prior art approach.

It is important to note that while both the isolation bridge flexure 44and the proofmass flexures 46, 48 are connected to isolation bridge 42,they remain separate from and entirely unconnected with one another. Atthe same time, the isolation bridge 42 is relatively rigid. Any stressesthat appear in frame 36 must pass through isolation bridge flexure 44and the isolation bridge 42 before they can ever reach proofmassflexures 46, 48 and certainly before they ever reach proofmass 12.Because of the rigidity of the isolation bridge and the flexibility ofthe isolation bridge flexure, most stresses that do travel toward theproofmass from the frame are substantially attenuated, if not entirelyeliminated, by the isolation bridge flexure and isolation bridge beforeever reaching the proofmass flexures. Thus, the isolation bridge and itsassociated isolation bridge flexure serve as a means of isolating theproofmass from the stresses in the frame. This is not only true ofassembly 10 but the other two assemblies to be described hereinafter. Itis also true for the proofmass assemblies illustrated in FIGS. 8 and 10of applicant's Parent Application.

A specific feature of support arrangement 14 over and above the factthat it uses an isolation bridge generally is that the isolation bridgeis connected to the isolation bridge flexure 44 and proofmass flexures46, 48 on the same longitudinal side. The opposite longitudinal side ofthe isolation bridge is not connected to any flexures or othercomponents, that is, it is free-floating. This is a first step in thedesign of support arrangement 14 to achieve bimetal stress cancellationof the flexures due to electrically conductive leads 22 which, in apreferred embodiment, have a different coefficient of thermal expansion,as noted heretofore. As a second step in this design, all of theflexures 44, 46 and 48 in the preferred embodiment are of substantiallythe same length and vary in width in accordance with a certain ratio. Asillustrated in FIG. 2, the combined width of the proofmass flexures 46,48 is W₁ while the width of isolation bridge flexure 44 is W₂. Thus, theratio W₁ /W₂ equals a specific ratio R. The third design criteria toachieve bimetal stress cancellation is that electrically conductiveleads 22 extending across the flexures do so across the lengths of theflexures parallel to one another so that the ratio of their widths alsoequals the same ratio R. As shown in FIG. 2, the combined sections 22'of lead 22 extending across each proofmass flexure have a combined widthW1' and the section 22" of lead 22 extending across the isolation bridgeflexure has a width W2'. Thus, W1' and W2' are provided so that theratio W1'/W2' also equals R.

This discussion immediately above has assumed that the two flexures 46and 48 are of the same width W 1/2 resulting in a combined W₁. It couldbe that the two flexures differ in width (resulting in the same combinedW₁). In this case, the width of the leads 22' would vary in the sameway. In order to achieve complete bimetal stress cancellation, inaddition to the requirements just recited, all of the flexures must beof equal thickness and free of stress from the frame or, for thatmatter, from the proofmass itself. Under this ideal situation, all thestresses resulting from the differences in the coefficients of thermalexpansion between leads 22 and the flexures will cancel each other outin the isolation bridge by causing the free-floating edge of the bridgeto flex sufficiently to eliminate those stresses. This is what is meantby bimetal stress cancellation.

As indicated above, bimetal stress cancellation presupposes that thereare no other stresses in the isolation bridge and proofmass flexures. Ifthere are, such stresses tend to interfere with the ability of theflexures and isolation bridge to achieve total bimetal stresscancellation. As a result, it is important to isolate the flexures fromrandom stresses. In the case of isolation bridge flexure 44, while itcannot be completely isolated from stresses in frame 34, frame section36 is configured to reduce the stresses introduced into the frame atmounting pads 40. Note specifically that flexure 44 is connecteddirectly to segment 50 of frame section 36. Segment 50 decreases inwidth significantly as a result of cutouts 52 between the isolationbridge flexure and mounting pads 40. By providing the cutouts, thetravel distance between the mounting pads and flexure 44 along framesection 36 is greater than it would be in the absence of cutouts 52 and,hence, this greater distance aids to further attenuate those stressesbefore the reach flexure 44. In the case of proofmass flexures 46 and48, any unwanted stresses in the main body 24 of proofmass 12 musttravel along legs 30 and 32 before they reach those flexures. Therefore,the stresses travel a greater distance to reach the flexures than theywould if the flexures were connected directly to edge 28 and, therefore,legs 30 and 32 aid in attenuating the stresses before they reach theflexures.

Still referring to FIG. 1, it is important to note that isolation bridge42 is located between the main body 24 of the proofmass 12 and all ofthe flexures 44, 46, 48. Legs 30 and 32 of the proofmass are especiallydesigned to make this possible. This particular "inside-out"configuration is to be distinguished from the proofmass assemblyillustrated in FIG. 10 in applicant's Parent Application. In thatassembly, the isolation bridge flexures and the proofmass flexures aredisposed between the proofmass and isolation bridge.

The inside-out configuration of support arrangement 14 illustrated inFIG. 1 has a number of advantages. It allows the overall assembly tooperate at a relatively high resonant frequency, for example, above 2000Hz, and at a relatively low angular spring rate. It also results inrelatively low stresses for loading along the pivot axis 16. As statedabove, in a preferred embodiment, the proofmass, frame, flexures and theisolation bridge are constructed of a single quartz wafer, which is avery high Q material, that is, a material that displays very low energylosses. Therefore, it is important that this integral arrangement ofcomponents does not reach its resonant frequency which would cause it tovibrate out of control. Hence, it is important that the overallarrangement be designed to display a high resonant frequency. At thesame time, the proofmass assembly is intended, for example, for use inan accelerometer which is a closed loop device. Therefore, anyelectronic errors are magnified and the higher the spring rate, thelarger these errors become. A similar error will occur if the proofmassassembly is used with force sensitive vibrating crystals. Hence, it isimportant to keep the assembly's angular spring rate relatively low.Also, stresses along the loading axis affect the cross couplingsensitvity of the device and, hence, loading stresses should also bekept low. As indicated above, the inside-out configuration of supportarrangement 14 makes it possible to achieve all of these objectives.

Turning to FIGS. 3 and 4, attention is directed to a pendulous type ofproofmass assembly designed in accordance with a second embodiment ofthis invention. This proofmass assembly is generally designated by thereference number 60 and includes a generally rectangular proofmass 62and an arrangement 64 supporting the proofmass for pivotal movement backand forth about a given axis 66 through a resting plane (the plane ofthe paper) which entirely contains the proofmass when the latter is atrest. Proof mass assembly 60 functions in the same manner as previouslydescribed assembly 10. Hence, reference is made thereto. In addition,like proofmass assembly 10, assembly 60 may include, for example, torquecoils and pickoff plates on opposite sides of proofmass 62 andelectrically conductive leads extending from the torque coils andpickoff plates to the outside world. In FIG. 3, proofmass 62 is shownincluding a generally rectangular main body 68 having a frontlongitudinal edge 70 and a back longitudinal edge 72. A pair of legs 74,76 extend rearwardly from opposite ends of edge 72.

Support arrangement 64, like the previously described supportarrangement 14, includes a frame 78 which circumscribes the proofmassand which includes its own mounting pads 80. The frame also includes agenerally T-shaped section 82 defined by a stem 84 and crossbar 86. Thesupport arrangement also includes two isolation bridges 88, 90, twoisolation bridge flexures 92, 94, and two proofmass flexures 96, 98.Isolation bridge flexure 92 and proofmass flexure 96 connect oppositeends of the same side of isolation bridge 88 to frame 78 and proofmass62, respectively. At the same time, isolation bridge flexure 94 andproofmass flexure 98 connect opposite ends of the same side of isolationbridge 90 to frame 78 and proofmass 62, respectively.

Note from FIG. 3 that the four flexures 92, 94, 96, 98 are all in linewith one another along axis 66. These flexures function in the samemanner as the previously described flexures to support proofmass 62 forpivotal movement back and forth about axis 66. In this regard, likeassembly 10, the proofmass, frame, isolation bridges and flexures alllie within the resting plane of the assembly in the absence of anysensing forces. In a preferred embodiment, all of these components arepreferably formed as an integral quartz wafer with the flexures etchedso that they are thinner than the rest of the components and therebyfunction in the intended manner.

It should be apparent that each of the isolation bridges 88 and 90 isfree-floating along its longitudinal edge opposite its associatedflexures. At the same time, the isolation bridge flexure and proofmassflexures supporting each isolation bridge are of substantially the samelength. Thus, as in assembly 10, the electrically conductive leadscrossing these flexures can be designed to provide bimetal stresscancellation. In FIG. 4, the isolation bridge 88 and its associatedflexures 92, 96 are shown with cooperating electrically conductive leadsegments 100 and 102. Note that isolation bridge flexure 98 is twice aswide as proofmass flexure 96. As a result, lead section 102 is madetwice as wide as lead section 100.

As stated in conjunction with assembly 10, in order for bimetalcancellation to be successful, in-plane stress in the flexures should bekept to a minimum. In assembly 60, note that any stress in the frameoriginating at the mounting pads must travel through T-shaped section 82including specifically, crossbar 86 before they ever reach flexures 92and 94. This T-shaped section helps to attenuate such stresses. At thesame time, legs 74 and 76 forming part of overall proofmass 62 helpattenuate stresses in the proofmass before they reach flexures 96 and98. This aids in assuring that bimetal stress cancellation issuccessful. In addition, two bridges rather than one, improves bimetalcancellation because the equality of flexure geometry applied only toeach isolation and proofmass flexure set separately and each pair ismore isolatd from frame stress than in the first embodiment.

Turning to FIG. 5, attention is directed to a pendulous type proofmassassembly designed in accordance with still another embodiment of thisinvention. This proofmass assembly, which is generally designated by thereference number 104, includes a generally rectangular proofmass 106 andan arrangement 108 for supporting the proofmass for pivotal movementback and forth about an axis 110. Proof mass assembly 104 operates in amanner similar to assemblies 10 and 60 and hence, its operation will notbe described herein.

Proofmass 106 is generally rectangular in configuration and includes afront edge 112 and a back edge 114. Unlike previously described proofmasses 24 and 26, proofmass 112 does not include any leg sections.

Support arrangement 108 includes a frame 116 which circumscribesproofmass 106 and which includes its own mounting pads 118. Arrangement108 also includes a single isolation bridge 120, a single isolationbridge flexure 122 and a single proofmass flexure 124. The isolationbridge flexure connects one side of the isolation bridge to frame 116and the proofmass flexure 124 connects the opposite side of theisolation bridge to proofmass 114. Like in the previous embodiments, theproofmass, frame, isolation bridge and flexures are preferablyintegrally formed as a single flat wafer of quartz with the flexuresbeing etched thinner than the other components to function in theintended manner.

It should be noted that isolation bridge 120, like the isolation bridgein FIG. 8 of applicant's Parent Application, is not free-floating. As aresult, this particular configuration will not sustain bimetalcancellation. As a result, this particular configuration is contemplatedfor use in proofmass assemblies that do not require electricallyconductive leads, that is, proofmass assemblies that use crystals torestrain their proofmass and where no static electrical discharge tracesacross the flexures are required. With particular regard to this latterpoint, while assemblies 10 and 60 are more suitable for use withelectronic restraining means, for example, torque coils and pickoffplates and associated electronics, it is to be understood that theycould also use quartz crystals for restraining purposes.

What is claimed:
 1. A pendulous assembly for use in an accelerometer orother such device which senses forces acting on the device in aparticular direction, said assembly comprising:(a) a proofmass; and (b)means supporting one end of said proofmass for pivotal movement about agiven axis back and forth through a resting plane which contains saidproofmass when the proofmass is at rest in the absence of any of saidforces, said supporting means including(i) a frame and means formounting the frame to a main support forming part of the force sensingdevice, (ii) an isolation bridge; (iii) isolation bridge flexure meansconnecting said isolation bridge with a section of said frame forpivotal movement of said isolation bridge back and forth about saidgiven axis; and (iv) proofmass flexure means separate from andsubstantially unconnected with said isolation bridge flexure means, saidproofmass flexure means comprising a pair of proofmass flexuresconnecting said proofmass with said isolation bridge for pivotalmovement of said proofmass back and forth about said given axis; (v)said isolation bridge flexure means and said proofmass flexure meansbeing aligned along said given axis with said isolation bridge flexuremeans positioned between said proofmass flexures.
 2. A pendulousassembly for use in an accelerometer or other such device which sensesforces acting on the device in a particular direction, said assemblycomprising:(a) a proofmass; and (b) means supporting one end of saidproofmass for pivotal movement about a given axis back and forth througha resting plane which contains said proofmass when the proofmass is atrest in the absence of any of said forces, said supporting meansincluding(i) a frame and means for mounting the frame to a main supportforming part of the force sensing device, (ii) an isolation bridge;(iii) isolation bridge flexure means connecting said isolation bridgewith a section of said frame for pivotal movement of said isolationbridge back and forth about said given axis; and (iv) proofmass flexuremeans separate from and substantially unconnected with said isolationbridge flexure means, said proofmass flexure means connecting saidproofmass with said isolation bridge for pivotal movement of saidproofmass back and forth about said given axis; (c) said proofmassincluding a main body and proofmass means connecting said main body withsaid proofmass flexure means such that the main body of said proofmassis located on the opposite side of said isolation bridge as saidisolation bridge flexure means and said proofmass flexure means.
 3. Anassembly according to claim 2 wherein(a) said isolation bridge iselongated, (b) said proofmass flexure means includes two proofmassflexures connected to opposite ends of said isolation bridge, and (c)said means connecting said main body with said proofmass flexure meansincludes two leg-like sections of said proofmass on opposite sides ofthe main body of said proofmass.
 4. An assembly according to claim 3wherein said isolation bridge flexure means includes a single isolationbridge flexure connected to said isolation bridge between said proofmassflexures.
 5. An assembly according to claim 4 wherein said frame sectionconnected to said isolation bridge by said isolation bridge flexureextends between said frame mounting means and includes a segment thereofwhich is adjacent to and joins the isolation bridge flexure and which isnarrower in width than said isolation bridge flexure.
 6. An assemblyaccording to claim 5 including electrically conductive leads located onend extending between said proofmass and said frame across said flexuresand said isolation bridge for carrying electrical signals from certaincomponents on said proofmass to cooperating components external of theproofmass assembly, said leads displaying a thermal coefficient ofexpansion different from that of said flexures.
 7. An assembly accordingto claim 6 wherein said isolation bridge flexure and said proofmassflexures extend parallel with one another and are of substantially equallength, wherein the combined width of said proofmass flexures and thewidth of said isolation bridge flexure display a specific ratio, whereinthe conductive leads on said flexures extend across the flexures instraight lines parallel with the flexures, and wherein the combinedwidth of the leads across said proofmass flexure and the width of thelead across said isolation bridge flexure display said specific ration.8. An assembly according to claim 7 wherein said flexures are planar inconfiguration and extend entirely in said resting plane when saidproofmass is at rest.
 9. A pendulous assembly for use in anaccelerometer or other such device which senses forces acting on thedevice in a particular direction, said assembly comprising:(a) aproofmass; and (b) means supporting one end of said proofmass forpivotal movement about a given axis back and forth through a restingplane which contains said proofmass when the proofmass is at rest in theabsence of any of said forces, said supporting means including(i) aframe and means for mounting the frame to a main support forming part ofthe force sensing device, (ii) an isolation bridge; (iii) isolationbridge flexure means connecting said isolation bridge with a section ofsaid frame for pivotal movement of said isolation bridge back and forthabout said given axis; and (iv) proofmass flexure means connecting saidproofmass with said isolation bridge for pivotal movement of saidproofmass back and forth about said given axis; (c) said proofmassincluding a main body and means connecting said main body with saidproofmass flexure means such that the main body of said proofmass islocated on the opposite side of said isolation bridge as said isolationbridge flexure means and said proofmass flexure means.
 10. A pendulousassembly for use in an accelerometer or other such device including anarrangement for sensing forces acting on the device in a particulardirection, said assembly comprising:(a) a proofmass; (b) means formingpart of said sensing arrangement and carried by or in direct engagementwith said proofmass for specifically sensing said forces acting on saidproofmass; and (c) means supporting one end of said proofmass forpivotal movement about a given axis back and forth through a restingplane which contains said proofmass when the proofmass is at rest in theabsence of any of said forces, said supporting means including(i) anisolation bridge support and means for mounting the isolation bridgesupport to a main support forming part of the force sensing device, (ii)at least one isolation bridge; (iii) isolation bridge flexure meansconnecting said isolation bridge with a section of said isolation bridgesupport for pivotal movement back and forth about said given axis; and(iv) proofmass flexure means connecting said proofmass with saidisolation bridge for pivotal movement of said proofmass back and forthabout said given axis; (d) said proofmass including a main body andmeans connecting said main body with said proofmass flexure means suchthat the main body of said proofmass is located on the opposite side ofsaid at least one isolation bridge as said isolation bridge flexuremeans and said proofmass flexure means.
 11. An assembly according toclaim 10 wherein(a) said at least one isolation bridge includes asingle, elongated isolation bridge, (b) said proofmass flexure meansincludes two proofmass flexures connected to opposite ends of saidisolation bridge, and (c) said means connecting said main body with saidproofmass flexure means includes two leg-like sections of said proofmasson opposite sides of the main body of said proofmass.
 12. An assemblyaccording to claim 11 wherein said isolation bridge flexure meansincludes a single isolation bridge flexure connected to said isolationbridge between said proofmass flexures.
 13. An assembly according toclaim 12 wherein said section of said isolation bridge support connectedto said isolation bridge by said isolation bridge flexure extendsbetween said mounting means and includes a segment thereof which isadjacent to and joins the isolation bridge flexure and which is narrowerin width than said isolation bridge flexure.
 14. An assembly accordingto claim 13 including electrically conductive leads located on andextending between said proofmass and said frame across said flexures andsaid isolation bridge for carrying electrical signals from certaincomponents on said proofmass to cooperating components external of theproofmass assembly, said leads displaying a thermal coefficient ofexpansion different from that of said flexure.
 15. An assembly accordingto claim 14 wherein said isolation bridge flexure and said proofmassflexures extend parallel with one another and are of substantially equallength, wherein the combined width of said proofmass flexures and thewidth of said isolation bridge flexures display a specific ratio,wherein the conductive leads on said flexures extend across theflexures, and wherein the combined width of the leads across saidproofmass flexure and the width of the lead across said isolation bridgeflexure display said specific ratio.
 16. An assembly according to claim15 wherein said flexures are planar in configuration and extend entirelyin said resting plane when said proofmass is at rest.